In laboratories, absorptiometer, spectrophotometer, nefelometer and fluorometer are generally used as methods to make this measurement. These measurement methods include various difficiencies which have been described in reports in the literature (for example, Clin. Chem. 19, 832, 1973, 20, 1028, 1974, and 21, 249, 1975).
These methods have been improved by the present invention so that the actual measurement can be accurately done. Likewise, the devices have been improved to be more and more automatic and the handling of the measurement results has been automatized (Anal. Chem. 48, 661, 1976).
Furthermore, the transportation and measurement of the reagents before the actual analysis is a great problem. The evaporation of liquid from the reagents and the samples before and during the measurement causes problems to which only little notice has been paid.
Today, both the samples and the reagents are pipetted either manually or automatically. The pipetting is based on volume measurement. The accuracy of the pipetting is usually of the order of .+-.1 .mu.l and often even poorer (Clin. Chem. 20, 320, 1974). Checking the pipetting result (getting feedback information) is naturally not possible. One must rely on the fact that the pipetting equipment has functioned properly each time and that the pipetter has been very careful each time.
In the literature, a device is described in which the liquid measurement is regulated by a computer. In this system, the weighing scale registers the weight for the liquids to be measured and the weighing scale is connected through the computer to a liquid measuring device in which the liquids to be measured can be regulated to a desired size with 1.0 mg. accuracy (Anal. Chem. 48, 661, 1976). In this system, the liquid evaporation problem has not been solved.
In the measurements described in the beginning, the samples, reagents and reaction mixture (sample and reagents) are usually water solutions or suspensions having characteristics (such as temperature, surface tension, diffusion standards and substance contents) which effect the water evaporation of these solutions. Circumstances of the environment (room temperature, relative humidity and ventilation) and the characteristic of the reagent or sample vessel (diameter, highness, tightness and material) which effect the shape of the liquid surface and so the surface area also effect how fast the liquid evaporates. Furthermore, the evaporation of the samples, reagents and reaction solutions effect the type and construction of the analyzer device in use greatly. Another factor is how much and how carefully trained the user of the device and samples, reagents and reaction solutions, is. The liquid (usually water) evaporation makes the content of other substances in suspension higher by percentage which is greater as the amount of water in the vessel at the beginning is decreased.
The evaporation in various stages cannot be ignored by assuming that it is always standard and that its effect is always the same. In the literature, it has recently been described that the evaporation of water from sample liquids in open vessels causes mistakes in the analysis. Examination of how much of the evaporation of samples and reagents occurs during the stages of the analysis which cause mistakes has not yet been made in total detail. Preliminary experiments show that the evaporation from the generally used cuvettes is about 1 mg./min. (the cuvette opening area is 1 cm.sup.2). In other words, if 1000 .mu.l reaction solution is preincubated 30 minutes, the evaporation during this period is 30 mg (about 3% of the reaction solution). This would cause a 3% error in the analysis result when measuring in a general photometer.